Fifty years ago, few people thought that smoking was actually good for you. An old slang term for cigarettes, after all, was “coffin nails.”

Even so, smoking was rampant throughout America — in workplaces, restaurants, on airplanes, anywhere people gathered. Commercials for cigarettes prominently aired on television, and more than 42 percent of adults smoked — including almost half of physicians. Nonsmokers just had to put up with it.

But the landmark report issued by U.S. Surgeon General Luther Terry on Jan. 11, 1964, put the official stamp of disapproval on smoking, definitively linking it to lung cancer, emphysema, heart disease and other illnesses and calling on the government to do something about it.

It’s hard to think of another action by government that has had such a long-range impact on public health in America. If anyone had been fooling themselves before, it was no longer possible to avoid the fact that smoking was “hazardous to your health.”

Although many Americans took the warning seriously and quit, the habit remained widespread. What finally started having a real impact on smoking rates was higher taxes driving up costs and activism by nonsmokers against secondhand smoke. They fought for smoking restrictions and, in Washington state and elsewhere, convinced voters to support bans in public places.

Although only about 18 percent of adults now smokes, that still translates into 43 million people. Smoking remains the No. 1 preventable cause of death, killing an estimated 443,000 Americans prematurely each year and having serious health impacts on another 8.6 million. And too many young people fool themselves into thinking that the habit somehow makes them look cool, and that it’s worth paying high prices and risking an early death.

Many smokers have switched over completely or partially to electronic cigarettes, which contain the addictive compound of nicotine but not the carcinogens and emit vapor, not harmful secondhand smoke. While e-cigarettes are a lower-risk alternative to regular cigarettes, it’s not clear whether the vapor discharged is completely safe for others to inhale. For that reason, all smoking restrictions should also apply to e-cigarettes.

The nation has made impressive inroads against smoking in the half-century since the surgeon general’s report. But there’s still much to be done. Discouraging young people from smoking should be the top priority, as it’s well-established that those who haven’t started smoking by age 18 are unlikely to become addicted.

Smoking exacts a ridiculously high toll in lives and health care costs; fighting it is still the most important public health mission facing the nation.